Explanation: The Gullies of Mars
would probably not have been
sensational
enough for the title of a vintage
Edgar Rice Burroughs
story about the Red Planet.
But it would get the
attention of planetary scientists today.
First identified in
high resolution images of Mars recorded
by the orbiting Mars Global Surveyor spacecraft,
the gullies
are interpreted as startling evidence that
liquid water
flowed across the martian surface in geologically recent
times.
Similar channels
on Earth
are formed by flowing water,
but on Mars
the temperature is normally too cold and the
atmosphere too thin to sustain liquid water.
Still, it is thought possible that water did burst out
from underground layers and remain
liquid long enough
to erode the gullies, while
alternative explanations
suggest the erosion was produced by a flowing
jumble of solid and gaseous carbon dioxide.
Spanning a few kilometers along the wall of an
impact crater
this high resolution image
from Mars Global Surveyor
shows typical martian gullies near the top of the crater wall
giving way to sand dunes toward the crater floor.
Whitish frost is visible near the top and on the dark sand
dunes below.
The muted colors were synthesized from wide angle image data.